.XPI file extension
To open .XPI files on Windows, if your goal is to install the add-on: open Firefox and use its Add-ons/Extensions manager to install the XPI (drag-and-drop may be blocked depending on Firefox settings/policy).
To open an .xpi file, install it in Firefox as an add-on (if it’s compatible and allowed), or open it as a ZIP archive to inspect its contents without installing.
Last updated: October 13, 2026
Open on your device
Choose your operating system for a dedicated step-by-step opening guide.
How to open .XPI files
Use these platform-specific instructions to open .XPI files safely.
Windows
- If your goal is to install the add-on: open Firefox and use its Add-ons/Extensions manager to install the XPI (drag-and-drop may be blocked depending on Firefox settings/policy).
- If you only want to view files: open the .xpi with a ZIP-capable archive tool and extract it to a folder to inspect files such as manifest/metadata and resources.
Mac
- To install (when permitted): use Firefox’s add-on installation flow (via the Extensions/Add-ons manager) and select the .xpi if Firefox offers a file picker.
- To inspect without installing: open the .xpi as a ZIP archive and extract it to a folder.
Linux
- To install (when permitted): use Firefox’s Add-ons/Extensions manager and install the .xpi through Firefox’s UI.
- To inspect: open/extract it with a ZIP tool; Linux desktops may map .xpi via the shared MIME-info database rules for extensions.
iOS
- iOS Firefox does not typically support installing desktop-style XPI extensions; treat the file as an archive and inspect it on a desktop system instead.
Android
- Android Firefox support for installing .xpi varies by Firefox channel/build; if installation is not offered, transfer the file to a desktop Firefox or inspect it as a ZIP archive.
Security notes
- Treat .xpi files as executable add-on packages, not just “documents”: installing an untrusted XPI can grant code running in the browser significant capabilities.
- XPIs are ZIP archives; inspecting/extracting them is safer than installing, but you should still avoid running any included scripts or binaries from unknown sources.
- Firefox add-ons can be signed and may include signing-related artifacts inside the XPI (for example under META-INF); missing/invalid signing can be a red flag (or simply indicate an older/testing build), and Firefox may block such installs depending on policy.
Can't open this file?
These are the most common causes and fixes when .XPI files fail to open.
Common reasons
- Firefox won’t install the XPI (blocked or incompatible)
- The XPI downloads but doesn’t install from a website
- Archive tools say the file is corrupt or won’t open
- Signature-related problems (unsigned or signature missing)
Fix steps
- Confirm the add-on is intended for your Firefox version and extension type (legacy vs. WebExtension packaging).
- Try installing through Firefox’s add-ons manager rather than treating it as a regular file.
- If it still fails, inspect the XPI as a ZIP to verify it contains the expected extension files/metadata.
OS-specific troubleshooting
What is a .XPI file?
An XPI is a ZIP-compressed archive used by Mozilla’s XPInstall system and for distributing Firefox extensions. Firefox can read resources directly from the XPI or unpack it, depending on how the add-on is built and how Firefox handles it. Because it is a ZIP container, many archive tools can open it for viewing.
Background
XPI (XPInstall) packages are the standard distribution format for Mozilla add-ons. In modern Firefox extension development, extensions are still packaged as standard ZIP files but distributed with the .xpi extension.
Common MIME types: application/x-xpinstall
Further reading
Authoritative resources for more details on the .XPI format.
Common .XPI issues
Firefox won’t install the XPI (blocked or incompatible)
Firefox may refuse an XPI if it is not compatible with your Firefox version or if installation from a file/source is restricted. Extension packaging and compatibility expectations changed significantly around Firefox 4 and later.
- Confirm the add-on is intended for your Firefox version and extension type (legacy vs. WebExtension packaging).
- Try installing through Firefox’s add-ons manager rather than treating it as a regular file.
- If it still fails, inspect the XPI as a ZIP to verify it contains the expected extension files/metadata.
The XPI downloads but doesn’t install from a website
Web servers may need to serve .xpi with the expected MIME type so browsers recognize it as an installable add-on package instead of a generic download.
- If you manage the website, configure the server to send the MIME type commonly used for XPI: application/x-xpinstall (as documented by Mozilla).
- If you are a user, save the file and use Firefox’s add-on installation flow; if that still fails, the add-on may be blocked or not compatible.
Archive tools say the file is corrupt or won’t open
An XPI is a ZIP archive; if download was interrupted or modified, ZIP tools may fail to read it.
- Re-download the .xpi from its original source to ensure it is complete.
- Try opening it with another ZIP-capable tool to confirm whether the archive is actually damaged.
- If it opens, extract to a folder rather than trying to view-in-place.
Signature-related problems (unsigned or signature missing)
Firefox add-ons use signing artifacts inside the XPI (for example under META-INF) and Firefox may enforce signing requirements depending on configuration/version.
- Inspect the XPI contents as a ZIP and check for signature-related files (such as entries under META-INF) if you are troubleshooting.
- If Firefox requires signed add-ons, obtain a properly signed build from a trusted source rather than trying to bypass checks.
FAQ
Is an .xpi file just a .zip file?
Yes. Mozilla describes Firefox extensions as standard ZIP files distributed with the .xpi extension, and XPInstall packages are ZIP-based installer modules.
What MIME type is used for .xpi files?
Mozilla documentation commonly refers to application/x-xpinstall for serving XPI over HTTP, but it is not an IANA-registered media type (it does not appear in the IANA media types registry index).
Can Firefox read files directly from the XPI, or must it unpack it?
Firefox can read extension contents directly from an XPI or unpack it, depending on how the extension is built and how Firefox handles it (as described in Mozilla’s Firefox 4-era extension update guidance).
Where do I look for signing information inside an XPI?
Mozilla’s extension signing documentation describes signature-related artifacts stored inside the XPI, including files under META-INF (for example META-INF/mozilla.rsa).
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